This invention provides a particular arrangement for the use of an afterburner in a smoke stack used in combination with a conventional domestic type of outdoor grill wherein a special air and gas flow system is produced around the cooking zone of such a domestic outdoor grill that delivers the effluent gasses selectively from above and/or from below the cooking zone to the afterburner positioned in a smoke stack. This gas flow system is preferably operative to first, substantially eliminate carcinogens which are known to be produced in the normal process of cooking on an outdoor grill from contact with the food being cooked on the grill, which carcinogens result from the reaction of grease dripping from the food being grilled which grease drips onto the fire bricks to be vaporized and ignited to burn which gaseous products normally flow upwardly with the heat flow from the glowing coals along with the products of combustion from the burning propane during this type of cooking process. Secondly, this invention also makes use of the afterburner in a stack means that may be built into or made to be attached to such grills to eliminate certain visible and other combustible pollutants that are usually found in the effluent from the cooking zone.
In the grill shown herein, the afterburner is positioned at the bottom of the smoke stack that is built integral with or added to the conventional form of a domestic outdoor grill in a position to collect all of the gasses flowing from the cooking area, the afterburner being situated directly in the mainstream of all of the combustion gasses flowing away from the cooking process. The height and diameter of the smoke stack are selected to produce a draft that normally removes all of the gaseous effluent flowing from the cooking zone and a damper control means is positioned to cooperate with the stack that causes the bulk of these gases to be removed from the heated cooking zone of the grill from a space below the food placed on its support over the fire bricks and preferably only a controlled and small proportion of the smoke arising from the grease dripping on the fire bricks is allowed to flow over the food on the grill to give the food a smoky flavor. Any of the gasses flowing upwardly from over the food and into the zone above the food is also removed by the draft produced by the stack means.
The afterburner is positioned at the bottom of the stack arrangement and beyond the cooking zone as it is here shown and serves to ignite the burnable, mostly carbon containing solid and combustible gaseous components, such as vaporized grease, carbon monoxide and possibly some minute solid food particles. These materials that normally escape from the heating means and the food being cooked that would otherwise be discharged into the atmosphere and at least some of which would be considered pollutants, are delivered past the afterburner to be ignited to be burned completely to form an invisible and innoxious gaseous discharge.
The afterburner here shown is provided to ignite these combustible materials to burn them in the excess oxygen carried over in the effluent gasses from the cooking process to convert these otherwise pollutants in the effluent into carbon dioxide and other forms of oxides that do not constitute pollutants in the discharge from the smoke stack The stack itself is situated in a position to vent its afterburner effluent above the head of the user of the grill.
One type of such a domestic gas fired outdoor grill has refractory bricks positioned below a food support upon which the food to be cooked is placed. These bricks are heated by a propane gas flame to provide radiant heat energy together with a flow of hot gasses upwardly toward and over the food for completing the cooking process. In such grills, the food being cooked is held spaced a suitable distance above the bricks and the usual melted drippings from the food fall through this space downwardly onto the brick. These drippings are then vaporized and the combustible components thereof are ignited and start to burn upon contacting the heated bricks. The resulting gaseous products normally flow upwardly to wash over the food being cooked and become a part of the usual gaseous effluent from the conventional cooking process as performed on the outdoor cooking grill.
A portion of this vaporized and sometimes burning grease is composed of the fats and oils melted from the usual meat products that are being cooked on such outdoor grills and the portion of the oily drippings that are ignited by the incandescent bricks under the food support not only add heat to the cooking process but in the conventional grill, some of the smoke particles in the burning drippings are deposited on the food on the support. While the absorption of some of the components of this smoke present in the flow of the burning drippings by the meat being cooked is considered to be desirable because they add flavor to the meat, it is now known that some carcinogenic products are entrained in the upwardly flowing vapors of the burning drippings which carcinogenic substances should preferably be eliminated or at least substantially prevented from having any contact with and absorption by the food being cooked.